1. Field of the Invention
The present invention relates generally to hearing prostheses, and more particularly, to objective fitting of a hearing prosthesis.
2. Related Art
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, an individual may have hearing loss of both types. In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. As such, those suffering from sensorineural hearing loss are thus unable to derive suitable benefit from conventional acoustic hearing aids. As a result, hearing prostheses that deliver electrical stimulation to nerve cells of the recipient's auditory system have been developed to provide persons having sensorineural hearing loss with the ability to perceive sound. Such electrically-stimulating hearing prostheses deliver electrical stimulation to nerve cells of the recipient's auditory system.
As used herein, a recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion cells, and regions of the brain used to sense sounds. Electrically-stimulating hearing prostheses include, for example, auditory brain stimulators and cochlear prostheses (commonly referred to as cochlear prosthetic devices, cochlear implants, cochlear devices, and the like; simply “cochlear implants” herein.)
Most sensorineural hearing loss is due to the absence or destruction of the cochlea hair cells which transduce acoustic signals into nerve impulses. It is for this purpose that cochlear implants have been developed. Cochlear implants electrically stimulate a recipient's cochlea by directly delivering direct electrical stimulation signals to the auditory nerve cells, thereby bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use an electrode array implanted in the cochlea to differentially activate auditory neurons that normally encode differential pitches of sound.
In contrast to sensorineural hearing loss, conductive hearing loss occurs when the normal mechanical pathways used to provide sound to hair cells in the cochlea are impeded, for example, by damage to the ossicular chain or to the ear canal. Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As a result, individuals suffering from conductive hearing loss typically receive an acoustic hearing aid. Acoustic hearing aids stimulate an individual's cochlea by providing an amplified sound to the cochlea, where the amplified sound causes mechanical motion of the cochlear fluid.
Unfortunately, not all individuals who suffer from conductive hearing loss are able to derive suitable benefit from hearing aids. For example, some individuals are prone to chronic inflammation or infection of the ear canal and cannot wear hearing aids. Similarly, hearing aids are typically unsuitable for individuals who have malformed or damaged outer/middle ears.
Those individuals who suffer conductive hearing loss, but cannot derive suitable benefit from hearing aids may benefit from devices which simulate natural hearing by generating displacement of the inner ear fluid, as occurs in normal hearing, without the need for operable outer and/or middle ears. Once such device is sometimes referred to as a mechanical stimulator herein. Mechanical stimulators are configured to generate a volumetric displacement of a recipient's inner fluid. This inner ear fluid displacement generates a traveling wave on the recipient's basilar membrane, thereby evoking a hearing response by the recipient.
Generally there is a need to fit mechanical stimulators, acoustic hearing aids and other hearing prostheses to a particular recipient. These fitting procedures generally rely upon interactive communication between an audiologist and the recipient.